1. Field of the Invention
This invention relates to an internal combustion engine, and more particularly to an internal combustion engine having a fuel injection device by which so-called stratified charge is accomplished at least during light load operation of the engine.
2. Description of the Prior Art
There has been known a stratified charge technique in which a fuel injection valve is provided in an intake passage and fuel is injected in the latter half of the intake stroke during light load operation of the engine so that rich air-fuel mixture surrounds the spark plug and lean air-fuel mixture surrounds the rich mixture, and so that the air-fuel mixture is given a swirling motion as it enters the combustion chamber, thereby suppressing diffusion of the stratified fuel in the compression stroke. See Japanese Unexamined Patent Publication Nos. 56(1981)-148636 and British Pat. No. 2,108,581, for example.
In the stratified charge, the mixture near the spark plug must be rich enough to be ignited by the spark plug, but the mixture remote from the spark plug may be very lean. Thus the stratified charge is advantageous in that the overall air-fuel ratio may be lean and accordingly the fuel economy can be improved and exhaust emissions can be reduced. Further, in the stratified charge, the mixture in the end gas zone is lean and hard to ignite and accordingly spark knock can be prevented.
On the other hand, the stratified charge involves a problem that, since the fuel is directly introduced into the combustion chamber before the fuel is sufficiently vaporized and atomized, the ignitability of the air-fuel mixture and the stability in combustion are adversely affected, especially when the engine is cold.